I want just to say that Arlendo is not the dowager empress’s son! Because she married the late emperor and Arlendo is the current emperor and empress son! So it is quite weird the influence she has on him, in my opinion...
by the way I really didn’t get why the Arabella will die for this unknown disease..., I mean, if this happens all the times why the duchess didn’t know before? Or, if it’s the first time, how could it be? And, another thing, if the Arabella has to die, why not tell Leslie to lose so her sister can win the role and die!! I didn’t get...

In any case I bet that if Leslie comes to be the Arabella her powers will defend her against the disease

it’d be a real shock for the dowager empress lolol
Edit: I found the answers to my question re-reading the chapter 63. If you don’t remember like me what’s happened you can check it. Now the question is why the dowager empress wants so much Arlendo is the emperor.... maybe he is her illegitimate son??